Various methods are known for producing low loss optical fibers for light sources emitting in the visible region of the electromagnetic spectrum. One such method is described, for example, in U.S. Pat. No. 3,884,550 issued to R. Maurer et al. The patent teaches the method of depositing high purity germania and silica by means of flame hydrolysis. The fiber exhibits good light transmitting properties over the visible region of the electromagnetic spectrum but exhibits strong attenuation in the vicinity of 0.95 .mu. in the infrared region.
U.S. Application Ser. No. 367,287 filed June 5, 1973 and assigned to the common assignee of the instant invention abandoned in favor of continuation Application Ser. No. 510,927 filed Oct. 1, 1974 in turn abandoned in favor of continuation Application Ser. No. 696,991 filed June 17, 1976. Recognized that the absorption at 0.95 .mu. was due to OH ions present in the fiber material of Maurer et al. The OH ions possibly resulted from water generated by the flame hydrolysis method of application of the core and cladding materials. The aforementioned U.S. application in an attempt to reduce the quantity of OH ions present in the fiber deposited the core and cladding materials in the absence of moisture by chemical vapor deposition within a carefully outgassed enclosure tube. The flame contributing to the thermal decomposition of the core and cladding materials was not allowed to contact these materials due to the interposition of the aforementioned tube. The dissociation of the core and cladding materials in the absence of moisture greatly reduced the quantity of OH ions in the finished fiber and diminished the absorption loss at 0.95 .mu..
With the continued improvements in the rated life of GaAs lasers the use of lasers as light sources in optical communications systems is also increasing. Since GaAs lasers principally emit in the infrared region of the electromagnetic spectrum, the absence of any absorption in the infrared region would greatly improve the overall optical communication efficiency.
The purpose of this invention is to provide methods and materials for producing optical fibers having substantially improved light transmission in the infrared region.